It looks like the only way to change a label on an edge e -- say
increment it -- is to read off the old one with G.E.label, then
remember the src and dst with G.E.src/dst, then G.remove_edge_e g e,
create a new edge e' with G.V.create src (label+1) dst, and
G.add_adge_e g e'. Is this supposed to be so complicated even for the
imperative graphs?
Cheers,
Alexy